Instead of some functions operating with hex strings,
and others using bytes, this consolidates most things to use bytes.
This mainly focuses on bitcoin.py and transaction.py,
and then adapts the API usages in other files.
Notably,
- scripts,
- pubkeys,
- signatures
should be bytes in almost all places now.
Previously all the interfaces used either "t" or "s".
Now the network only tries to use "s" for all interfaces, except for
the main interface, which the user can manually specify to use "t".
(so e.g. if you run with "--server localhost:50002:t", the main server will use "t",
but all the rest will use "s")
